Reed switch

ABSTRACT

A switching device such as a reed switch having moving contacts whose outer contacting surface consists of an outer layer of metal such as ruthenium or rhodium having thickness of from 0.1 to 5.0 Mu m with an interrupted or non-interrupted underlayer of at least 1 percent by volume of non-metal.

United States Patent Steinmetz et al.

[451 May to, 1972 REED SWITCH Anthony Steinmetz; Douwe Mindert de Boer, both of Hilversum, Netherlands Assignee: U.S. Philips Corporation, New York, N .Y.

Filed: Aug. 21, 1970 Appl. No.: 66,008

Inventors:

Foreign Application Priority Data Aug. 29, 1969 Netherlands 6913194 June 10, 1970 Netherlands ..7008388 us. Cl. ..200/l66 0, 29/630 0 Int. cl. ..H0lh 1/66 Fieid of Search ..200/l66 0; 29/630 c JOOOOOOOOOOOOOD References Cited UNITED STATES PATENTS 2,734,979 2/1956 Higley ..200/l66 C X 2,070,321 2/1937 Slezak..... ..200/l66 C Primary Examiner-H. 0. Jones Attorney-Frank R. Trifari [5 7] ABSTRACT A switching device such as a reed switch having moving contacts whose outer contacting surface consists of an outer layer of metal such as ruthenium or rhodium having thickness of from 0.1 to 5.0 pm with an interrupted or non-interrupted underlayer of at least! percent by volume of non-metal.

8 Claims, 2 Drawing Figures a U U U U U U U U U U U u Patented May 16, 1972 3,663,777

I /ooouuuouuuuy Fig. l

/MOVING CONTACT ELEMENT ll l3 lNNER suRFAca bzfi |4 OUTER F K-CONTACT SURFACE Fig. 2

m wavy (ms. ANTHONY STEINMETZ DOUWE MINDERT DE BOER BY REED SWITCH The invention relates to a switching device having moving contacts in recent years such devices having reed contacts in a hermetically closed envelope in miniaturized form have been frequently used in modern telephone exchanges, computer systems and date transmission systems. The contact members in these switching devices are generally provided at the ends of resilient conductors in a closed space filled with a protective gas. The conductors consist of magnetic material so that the contact may be opened or closed with the aid of coils or permanent magnets provided outside the envelope, other forms of switching devices having contacts which are either or not enveloped are relay or cross-bar switches.

Very stringent requirements as regards lifetime, both in unloaded and loaded conditions are imposed on all these devices while the contact resistance must be low and constant throughout the life of the device. In known devices it has not been managed until now to meet the imposed requirements completely.

It is known from U.S. Pat. No. 2,600,175 that the outer surfaces of contacts consist of noble metal, forexample, ruthenium.

Microscopic tests of these contact surfaces upon switching revealed that dot-like and crater-like contact erosion occur while in addition the contacts often got stuck.

According to the invention a switching device includes moving contacts of which at least the contact surface is clad with a contact cladding which consists of at least two layers, the outer one comprises metal having a thickness of from 0.1 to nm while an uninterrupted or interrupted layer comprising at least 1 vol. percent of non-metal is provided directly or not directly underneath said layer.

In an advantageous embodiment, of the combination of layers the layer, comprising the non-metal consists completely of carbon, graphite, phosphorus, sulphur, silicon or metal oxide having a thickness of from 0.001 to 1 pm while the outer layer consists of ruthenium or rhodium.

A further usable embodiment has the non-metal present in a finely divided form in a metal having a melting point of less than 1,500 C. at a layer thickness of at least 0.1 m while the outer layer consists of ruthenium or rhodium.

It was found that when'using the contact cladding according to the invention, plane contact erosion instead of dot-like and crater-like erosion occurs. Since substantially the entire contact surface is used in this manner in contrast with a very small portion in case of the dot-like and crater-like erosion, a considerable extension of the lifetime by a factor in the order of 100 is obtained. It is essential that also the lifetime is very long in case of unloaded switching. A numberof switching operations of 10 may be achieved without noticeable increase of the contact resistance.

A further advantage of the embodiment in which metal, includes finely divided non-metal is that they rebound only to a slight extent upon closing. Contacts coated with uncontaminated gold rebound approximately 20 times, and tungsten-coated contacts even rebound up to 30 times upon closing. Some metalnon metal layer combinations according to the invention limit the rebound effect to only one to four times. This, too, considerably contributes to the extension of the lifetime of the contacts.

It is to be noted that contact materials are known from Swiss patent specifications 229,890 and 237,872 which materials consist of a pressed and sintered mass obtained from a pulverulent noble metal including an addition of for example graphite, silicon, cadmium oxide or lead oxide. Layer thicknesses of several microns are difficult to control in sintering techniques which control is particularly important for microcontacts. It is true that layers of this kind show plane contact erosion when they are provided in thin layers, but without a surface layer of metal according to the invention the contacts do not have satisfactory properties upon unloaded switching due to an unstable level of the resistance especially after switching over a long period, and the contacts have a great tendency to get stuck.

The techniques by which the combination of layers according to the invention may be provided are cathode sputtering, vapor deposition, electrodeposition, electrophoresis or a combination of the latter two techniques, such as the joint deposition of a metal and a non-metal, the latter being enclosed in a finely divided form in the metal deposition.

One embodiment of the switching device according to the invention which is still to be noted, is the one in which the non-metal is present in a finely divided or laminated form in gold which is largely diffused into the material consisting of a magnetic Fe-Ni alloy by means of heating in a protective gas or m vacuo.

The invention will further be described in detail by way of several examples in conjunction with FIGS. 1 and 2 of the drawing.

EXAMPLE 1 Reed contacts l0, 11 whose parts to be sealed within the envelope 12 were approximately 7 mm long and 0.5 mm wide comprising magnetic nickel-iron were coated in a conventional cathode sputtering device with an inner layer 13 of Au including 2 percent by weight of carbon having a thickness of 3 pt. For this purpose a cathode was used comprising the sintered pulverulent materials in the same weight ratio. The argon pressure during sputtering was 10 mm Hg, the voltage was 2,000 volt and the current was 0.5 A.

The reed contacts thus coated were also coated by means of cathode sputtering with an outer layer 14 of ruthenium having a thickness of 0.5

The reed contact were subsequently sealed pairwise in a glass envelope and were life-tested using current loads of up to mA and voltages of up to 100 volts and in unloaded condition. In all these cases lifetime values expressed in numbers of switching operations were found to be ranging from 1 X 10 to 100 X 10.

EXAMPLE 2 Reed contacts having dimensions and comprising material in accordance with Example 1 were coated with a layer 13 by means of cathode sputtering. The cathode comprises Au including 5 percent by weight of Ni. Sputtering took place in an atmosphere of argon including 10 vol. percent of propane at a pressure of 10" mm Hg. The voltage was 2,000 volts and the current was 1.5 A. The thickness of the layer 14 obtained was 3 ;1.. Subsequently a layer of ruthenium was provided likewise by means of sputtering. The contacts obtained have properties which are analogous to those according to Example 1 EXAMPLE 3 Reed contacts whose parts to be sealed within the envelope were approximately 17 mm long and 0.5 mm wide comprising magnetic nickel-iron were coated in a conventional cathode sputtering device with a layer of Ru having a thickness of 3 pm. The argon pressure during sputtering was 10 mm Hg, the voltage was 2,000 volts and the sputtering current was 1 A.

The reed contacts thus coated were also coated likewise under the same conditions by means of cathode sputtering with a layer of carbon having a thickness of approximately 0.05 pm.

Subsequently, again under the same circumstances, a layer of gold-carbon having a thickness of 1 pm and finally a layer of Ru having a thickness of 0.1 pm were provided.

The reed contacts were finally sealed pairwise in a glass envelope and were life-tested at current loads of up to 100 mA at peak currents of up to 1 A and more and voltages of up to 100 volts and in unloaded condition. In all these cases lifetime values expressed in numbers of switching operations were found to be ranging form 1 X 10 to 10 X 10 in loaded condition and to 100 X 10 in unloaded condition.

EXAMPLE 4 Reed contacts having dimensions and comprising material in accordance with Example 1, were coated in the same manner with a layer of Ru having a thickness of 3 am, and subsequently with a layer of carbon having a thickness of 0.05 pm by means of cathode sputtering. Subsequently, a thin layer of gold having a thickness of 0.1 gm was provided likewise by means of sputtering. The contacts obtained have properties which are analogous to those of Example 1 EXAMPLE 5 Reed contacts of the same material as in Example 1 were successively coated with a 1 m thick ruthenium layer, a 0.05 m thick carbon layer, a 1 pm thick ruthenium layer, a 0.05 pm thick carbon layer and a 1 gm thick ruthenium layer. The contacts thus manufactured had a lifetime of the same order as those in accordance with the other examples but at loads of up to 1 A.

EXAMPLE 6 Reed contacts whose parts to be sealed within the envelope were approximately 17 mm long and 0.5 mm wide comprising a magnetic nickel-iron alloy of the composition 50 percent by weight of Fe and 50 percent by weight of Ni were coated with a 3 pm thick deposit with the aid of a gold-plating bath comprising per liter 10 g CoSO 55 g citric acid 60 g primary potassium phosphate and g ethylene diamine tetra acetic acid. at a bath temperature of to C. and a current density of l to 3 A sq.dm. Subsequently the reed contacts were heated for 30 minutes in hydrogen-containing nitrogen at a temperature of between 600 and 900 C.

After cooling the contacts were coated with a layer of ruthenium having a thickness offrom 0.1 to 1 ,urn.

Subsequently the reed contacts were sealed pairwise in a glass envelope and were lifetested at a load of 1, 10 and 100 mA and unloaded. In all these cases lifetime values expressed in numbers of switching operations were found to be ranging from 1 X l0 to l00 10 What is claimed is:

1. In a reed switch including a sealed envelope with two moving contacts disposed therein, each contact formed of magnetic nickel-iron having a contact surface comprising at least two layers, the outer exposed layer being a metal of thickness in the range of 0.1 to 5.0 ,um, and an underlayer being a non-metal.

2. A device according to claim 1 wherein the non-metal underlayer has thickness in the range of 0.001 to 1.0 am from the group consisting of carbon, graphite, phosphorous, sulphur, silicon, and metal oxide, and the outer layer comprises ruthenium or rhodium.

3. A device according to claim 1 wherein the underlayer comprises a non-metal present in a finely divided form in a metal deposition having a melting point of less than 1,500 O, in a layer thickness of at least 0.1 pm, and that the outer layer consists of ruthenium or rhodium.

4. A device according to claim 1 wherein the non-metal is present in finely divided form in gold which is largely diffused into the basic material.

5. A device according to claim 1 wherein said underlayer is an uninterrupted layer.

6. A device according to claim 1 wherein said underlayer is an interrupted layer.

7. A device according to claim 1 wherein the non-metal is present in laminated form in gold which is largely diffused into the basic material.

8. In a reed switch including a sealed envelope with two moving contacts disposed therein, each contact comprising a base formed of magnetic nickel-iron having a contact surface formed of at least two layers, an outer exposed layer consisting of ruthenium or rhodium of thickness in the range of 0.1 to 5.0p.m, and an under layer between the base and outer layer formed of carbon. 

2. A device according to claim 1 wherein the non-metal underlayer has thickness in the range of 0.001 to 1.0 Mu m from the group consisting of carbon, graphite, phosphorous, sulphur, silicon, and metal oxide, and the outer layer comprises ruthenium or rhodium.
 3. A device according to claim 1 wherein the underlayer comprises a non-metal present in a finely divided form in a metal deposition having a melting point of less than 1,500* C., in a layer thickness of at least 0.1 Mu m, and that the outer layer consists of ruthenium or rhodium.
 4. A device according to claim 1 wherein the non-metal is present in finely divided form in gold which is largely diffused into the basic material.
 5. A device according to claim 1 wherein said underlayer is an uninterrupted layer.
 6. A device according to claim 1 wherein said underlayer is an interrupted layer.
 7. A device according to claim 1 wherein the non-metal is present in laminated form in gold which is largely diffused into the basic material.
 8. In a reed switch including a sealed envelope with two moving contacts disposed therein, each contact comprising a base formed of magnetic nickel-iron having a contact surface formed of at least two layers, an outer exposed layer consisting of ruthenium or rhodium of thickness in the range of 0.1 to 5.0 Mu m, and an under layer between the base and outer layer formed of carbon. 